1. Field of the Invention
The present invention relates an interlocking change-over valve system. More specifically, the present invention relates to an interlocking change-over valve system for use in a hydraulic control mechanism such as a rotary bucket mounted on a swing arm of a power-assisted shovel truck.
2. Discussion of the Related Art
Conventional hydraulic valve control mechanisms for use in power-assisted shovel trucks or jib cranes include a plurality of independent valves. The valves are activated and controlled directly or indirectly by an operator located within a gondola of the truck or crane. Often, electromagnetic spool valves are used, requiring difficult fine adjustments and causing vibrations to occur.
When a rotary bucket, as disclosed in, for example, Japanese Patent Laid-Open Nos. 207728/1986 and 240295/1987, is mounted on the front end of a swing arm of the shovel truck, a large number of hydraulic actuators (hydraulic cylinders, hydraulic motors, etc.) are needed as the bucket requires movement in a variety of directions. However, as the number of hydraulic actuators increases, the hydraulic pressure typically decreases. As a result, operations slow or the force of operation weakens when a multitude of hydraulic actuators are used simultaneously unless the hydraulic pressure source, such as an oil pump or a hydraulic pressure tank, is very large.
In addition, in conventional spool valves, the pilot hydraulic pressure and the hydraulic pressure for operation pass through a complex network resulting in high pressure loss and slow operation. Moreover, electromagnetic valves, which permit the passage of large amounts of pressurized fluid, are very expensive and difficult to employ.